Tens of thousands of dollars in medical marijuana can be rendered useless if samples are found to contain toxins that could trigger respiratory infections, sinusitis or worse.

There is no Food and Drug Administration for marijuana. So the private lab fills a profitable niche in a trade operating without regulatory oversight.

"This is a success story of self-regulation," said Addison DeMoura, Steep Hill Lab's co-founder. "We want people to produce cannabis that they would give to the dearest person they love."

No state rules in California require medical marijuana be tested. While few pot businesses want a rap of toxic weed, no inspection regimen ensures they remove tainted products.

Steep Hill Lab says 3 percent of the pot it tests has unsafe mold levels under general guidelines for herbal products. Eighty-five percent show traces of mold.

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The medical pot community has cause for seeking assurances that the marijuana being peddled is free of toxins that can develop during growing, drying or packaging.

A 2008 guidebook, "The Marijuana Medical Handbook," warns of Aspergillus, a mold that can appear in marijuana and numerous other agricultural products. It can be dangerous for seriously ill people, such as AIDS and cancer patients using pot to treat nausea or other side effects.

"There have been reports of aspergillosis, a lung infection caused by inhalation of spores from the Aspergillus fungus," wrote California marijuana researchers Dale Gieringer and Ed Rosenthal and Washington physician Gregory Carter.

A 1988 study published by the American College of Chest Physicians focused on a pot-smoking leukemia patient in Philadelphia whose death was hastened by an infection caused by moldy marijuana.

Recently, tests on pot that undercover police officers bought from a Los Angeles dispensary revealed an insecticide, bifenthrin, that registered 170 times "tolerable" guidelines set by the Environmental Protection Agency for human food or animal feed.

"You may have no idea what it's been treated with," said Assistant Los Angeles City Attorney Asha Greenberg. Authorities speculated the dispensary sold pot smuggled across the border or grown illicitly.

Los Angeles now requires pot dispensaries to test for pesticides or "any other regulated contaminants" for foods or drugs.

A leading San Francisco physician said most medical pot in California is safely grown and poses no health risk.

"That whole story of people getting fungal infections from inhaling marijuana is an old wives' tale," said Dr. Donald Abrams, chief of oncology at San Francisco General Hospital and a researcher in state-funded studies on marijuana's usefulness for chronic pain.

But Abrams said Steep Hill may help establish dosing protocols for marijuana so that users can know how much they should smoke.

As a result of tests at Steep Hill, Harborside Health Center, a cannabis club that serves 47,000 medical users at dispensaries in Oakland and San Jose, lists tetrahydrocannabinol (THC) levels for each pot strain it provides. THC is the psychoactive ingredient in marijuana.

DeMoura, a marketing representative and former pot dispensary operator from Stanislaus County, started the lab with David Lampach, a former Wall Street equities trader and marijuana cultivator from Mendocino County.

Lampach operates a gas chromatography machine that separates marijuana compounds for testing and a mass spectrometer that identifies ingredients and potency.

"This is the gold standard for measuring active agents," he said.

Bay Area pot growers, dispensary operators and researchers have their own safety group, the Medical Cannabis Safety Council, a Bay Area group of pot growers, dispensary operators and researchers.

"We're not trying to scare people," said Janet Weiss, a toxicologist who works with the Steep Hill Lab. "We're saying this industry should join the rest of the world in what food and drugs are required to do. It shouldn't be a buyers-beware market."